Fabrication of hollow articles



Dec. 11, 1962 R. M. NEEL ETAL 3,067,491

FABRICATION OF HOLLOW ARTICLES Filed Dec. 10, 1956 E [i 1 I, I A A 0554/. I254 I Mz/c Z/m m I 4 imam ME bang d.

Ivar/67% United States Patent 01 3,067,491 FABRICATION OF HOLLOWARTICLES Robert M. Neel, New Douglas, and Ulric R. Jaeger, Alton, Ill.,and Clarence A. Isbell, Jr., Ferguson, Mo.

Filed Dec. 10, 1956, Ser. No. 627,290

4 Claims. (Cl. 29-1573) This invention relates to the fabrication ofhollow articles and more specifically to forming the hollows in sucharticles.

In the fabrication of hollow sheet metal panels by one well knownprocess, two sheets of metal are arranged in stack-like fashion with adesign of weld-inhibiting material applied to a portion of one of theadjacent faces of the sheets. The sheets are secured together to preventrelative slippage and are then welded together in their adjacent areasnot separated by the weld-inhibiting material, in any suitable manner,such as by hot rolling. As the sheets are being welded together by hotrolling, they are elongated in the direction of rolling and thereforethe design of weld-inhibiting material must be foreshortened in theintended direction of rolling when it is applied to the sheet. After thesheets are welded together they are usually softened as by annealing andthe unjoined portion to which the weld-inhibiting material has beenapplied is outwardly expanded, as by injecting therein a fluid pressureof sufficient magnitude to permanently distend the sheets in the areaadjacent to the weld-inhibiting design. The Weld-inhibiting design mayassume any desired configuration, for example, a design which willdefine, after expansion of the blank, a fluid conveying circuit of thetype required in refrigerator heat exchanger panels. The aforementionedprocess is more fully described in U.S. Patent 2,690,002, issuedSeptember 28, 1954.

This invention is directed to the fabrication of hollow articles havinga partially smooth side and an opposite fully distended side, by weldingtogether sheets having different strength characteristics, ordifferentiable elastic properties and if necessary adequatelydifferentiating the elastic properties prior to expanding the blank. Theblank thus formed is clamped between a pair of spacedapart hard pressurepads with a compressible pressure pad inserted between a portion of theunjoined area of the blank and one of the hard pressure pads, orpreferably a compressible pad next to the blank and a hard shim betweenthe compressible pad and the hard pressure pad, and then expanding theblank by injecting into the unjoined portion thereof a fluid pressure ofsufficient magnitude to permanently distend the blank into firmengagement with the spaced-apart hard platens. The hard pressure padsare spaced apart a distance such that upon expansion of the unjoinedportion of the blank the resultant distended portions firmly engage thehard pressure pads and the portions of the distentions which engage thehard pressure pads are thereby flattened. The resultant distentions onthe portion of the side of the blank in engagement with the compressiblepressure pad are impressed into the compressible pressure pad. Thecompressible pressure pad tends to hold the side of the blank oppositethereto firmly against the hard pressure pad and in conjunction with thedifferent strengths of the sheets this is suflicient to prevent outwarddistention of the unjoined portion of the blank on the side opposite thecompressible pressure pad so that this side is smooth. To obtain themaximum volume in the hollow portion of the expanded panel the pressureshould be such as to permanently distend the weaker sheet under thecompressible pressure pad, between its elastic limit and ultimaterupture strength, but below the combined effect of the elastic limit ofthe stronger sheet acted upon by the compressible pressure pad and theholding eflect of the compressible ice pressure pad. It is to be notedas indicated above that this pressure is, however, suflicient to distendthe remainder of the hollow portions of the panel, not acted upon by thecompressible pressure pad, firmly against the hard pressure pads.

As used herein the term smooth refers to a surface devoid of depressionsor protrusions in the overall general configuration of the surface. Theterm elastic limit refers to the maximum stress that a material willwithstand without permanent deformation.

This invention is directed primarily to the expansion of metal panelsfrom blanks fabricated with an unjoined interior portion, but theinvention is equally applicable to similiar panels fabricated frommaterials other than metal, such as various plastics, and to panelsfabricated from dissimilar materials such as metal and a plastic joinedtogether with an unjoined portion between the sheets.

It is an object of this invention to fabricate an improved hollow panelwith one side partially smooth and the opposite side distended.

Another object of this invention is to fabricate an improved panelhaving formed therein a hollow portion, such as fluid carrying conduits,defined by a partially smooth surface and an opposite surface havingprotrusions conforming to the hollows.

Another object of this invention is to fabricate a hol low panel inwhich a portion of one side is smooth and the remaining portion of thisside and other side is distended.

Another object of this invention is to provide a method of fabricatinghollow panels in which a portion of one of the outer surfaces is smoothin the areas adjacent an unjoined interior area of said panel.

Additional objects and advantages will be apparent from the followingdescription and drawings in which:

FIGURES l and 2 indicate schematically a process for fabricating a blankfrom which a hollow smooth-sided panel may be subsequently formed, andmore specifically;

FIGURE 1 is a perspective view of a sheet of material having applied tothe surface thereof a pattern of weldinhibiting material;

FIGURE 2 is a perspective view of the sheet shown in FIGURE 1 with asecond sheet superimposed thereon in laminar fashion and tacked theretoas by spot welding, the sheets having differentiable strengthcharacteristics, with the pattern of weld-inhibiting material sandwichedbetween the sheets and showing the sheets being welded together in arolling mill to form a blank;

FIGURE 3 is a longitudinal sectional schematic view of the resultantblank of FIGURE 2, the line 33 in FIGURE 1 indicating the portion of theweld-inhibiting pattern shown in FIGURE 3, and showing the blankpositioned between a pair of pressure pads;

FIGURE 4 is a transverse sectional view of the resultant hollow panelafter the unjoined portion of the blank has been expanded, the sectionof the panel being indicated by the line 44 in FIGURE 6 of the entirefinished panel;

FIGURE 5 is a sectional view of another portion of the finished paneltaken on the line 55 in FIGURE 6;

FIGURE 6 is a perspective view of one side of the expanded panel, and;

FIGURE 7 is a perspective view of the opposite side of the expandedpanel shown in FIGURE 6.

Referring to FIGURE 1 of the drawings, a sheet 1, such as aluminum orcopper, has applied to a clean surface 2 a design 3 of Weld-inhibitingmaterial. The weldinhibiting design 3 includes a pair of header areas 4interconnected by conduit strips 5. The strips 5 may have a wide portion6 at their midportion. The weldinhibiting design 3 includes a strip 7interconnecting a portion of the aforementioned design with an edge 8 ofthe sheet 1. In this instance, the strip 7 interconnects the edge 8 ofthe sheet and one of the header areas 4. A second sheet 9 ofdifferential strength from the first sheet 1, is superimposed on thesurface 2 of the first sheet with the weld-inhibiting pattern 3sandwiched between the sheets. The two sheets are then tacked togetheras by spot welding 11 to prevent relative slippage of the adjacentsurfaces of the sheets during a subsequent welding operation. After thesheets have been tacked together they are welded together along theiradjacent surfaces not separated by the weld-inhibiting material 3. Onewell known method of welding the sheets together is by hot rolling, inwhich the sheets are first heated and then passed through mill rolls 12,between which they are reduced in thickness and elongated in thedirection of rolling. If desired, the resultant blank 14 having anunjoined interior portion 15 may be softened in any appropriate manneras by annealing and thereafter the blank may be cold rolled to provide amore even thickness and again annealed. The inlet portion 7 ofweld-inhibiting material produces an unjoined inlet 16 into the unjoinedheader and conduit design after welding the sheets together to form ablank.

The sheets 1 and 9 are selected so that one of the sheets will have agreater strength than the other sheet. Either sheet may be the weaker,and sheet 9 will be designated the weaker sheet for purposes of thesubsequent description. The sheets may be of the same material but ofdifferent thicknesses, and therefore of different strength. When theblank has been fabricated of materials having diiferent inherentstrength characteristics, a controlled annealing process may be requiredin which one of the sheets is fully annealed whereas the other sheet issubstantially unafiected by the annealing treatment. With certaincomposite copper or aluminum blanks an annealing to soften one of thesheets may be required along with a heat treatment to harden the othersheet. Such methods of sheet differentiating treatments will be morefully discussed hereafter.

For any given pair of sheets the effect of heat treatment may bedetermined from an appropriate handbook such as Metals Handbook, 1948edition, published by The American Society for Metals, Cleveland, Ohio.In addition to copper and aluminum, steel and stainless steel of thesame or different characteristics are particularly suitable for thefabrication of smooth sided hollow metal panels. In any event, theresultant blanks have one relatively weaker side which may bepermanently distended at a pressure too low to permanently distend theother stronger side.

The following examples set forth the treatment of but a few of the manypossible combinations. The examples refer to yield strength rather thanelastic limit, however, the elastic limit, which is slightly less thanthe yield strength, may be determined on the basis of the yield strengthfor any given metal, by methods well understood in the art.

Example 1 material is applied to a surface of one of the sheets and thissurface is then welded to a surface of the other sheet in the areas notseparated by the weld-inhibiting material by hot rolling at atemperature of 1700 F., and a reduction of 60% in a single pass througha rolling mill. Subsequently, the Welded blank may be fully annealed andthen cold rolled to an additional reduction of 30% after which it is inthe work hardened state having a hardness 4 of 60 Rockwell B and a yieldstrength of 55,000 p.s.i. for the high conductivity alloy and a hardnessof 87 Rockwell B and a yield strength of 67,000 p.s.i. for theelectrolytic tough pitch alloy. The blank is then heated at atemperature of 300 C. for 60 minutes fully annealing the electrolytictough pitch alloy. This temperature is below the annealing temperatureof 650 C. for the high conductivity alloy. The electrolytic tough pitchalloy has then been annealed to a yield strength of about 7,000 p.s.i.The high conductivity alloy retains a yield strength of about 56,000p.s.i.

Example- 2 In a blank fabricated from two sheets of aluminum alloy, thefirst commercially pure aluminum (1100 alloy), and the second 6061aluminum alloy, a pattern of weldinhibiting material is applied to theclean face of one of the sheets and this face is welded to a clean faceof the other sheet in the areas not separated bythe weld-inhibitingmaterial by hot rolling at a temperature of 950 F., and a reduction of65% in a single pass through a rolling mill. Subsequently, the weldedblank is fully annealed and cold rolled at a reduction of 27%. Exceptfor obtaining a weld and a blank of even thickness, the previousannealing and cold rolling steps have no effect on the mechanicalproperties of either side of the blank after the following heattreatments. The blank is solution heat treated by holding the entiremass of the blank at a temperature of 970 F. for 10 minutes, followed byan immediate quenching, within five seconds of being removed from thefurnace, in water at a temperature of about 50 F. The 1100 alloy is nowfully annealed to a 0 temper and the 6061 alloy has now been solutionheat treated to the T-4 temper. The blank is next precipitation heattreated to either a temperature of 320 F. for 16-20 hours, or atemperature of 350 F. for 610 hours which yields the same results. The1100 alloy now has a yield strength of 5,000 p.s.i. and the 6061 alloynow has a yield strength of 40,000 p.s.i. both at an offset of 0.2%.

Referring to FIGURE 3, a compressible pressure pad 18 is positioned onthe top surface of the blank 14 and a hard shim 19 is positioned on topof the pad 18. The blank, compressible pressure pad, and shim arepositioned between a pair of hard pressure pads 20, and a fluid pressureconveying nozzle 21 is inserted into the inlet 16 in the blank. The hardpressure pads 20 are respectively secured to a fixed jaw 22 and avertically movable jaw 23 of a press 24. The movable upper jaw 23 issecured to a plunger 25 received in a cylinder 26 with a fluid-tightsliding fit. The movable jaw 23 is maintained in a raised position inany appropriate manner as by a spring 27 engaging a shoulder 28 on thelower end of the cylinder 26 and a shoulder 29 on the plunger 25. Thecylinder 26 is fixed with respect to the lower jaw 22 of the press inany appropriate manner as by arms 31. A fluid pressure conveying conduit32 opens into the upper end of the cylinder 26 for injecting a fluidinto the cylinder thereby forcing the plunger 25 downward and the hardupper pressure pad toward the hard lower pressrue pad and shim 19. Thehard pressure pads 20 are spaced from each other. The spacing may beadjusted as by shims 33 and the spacing is such that the upper hardpressure pad does not engage the blank 14. However, the compressiblepressure pad 18 and shim 19 are clamped between the blank 14 and thehard upper pressure pad 20. The unjoined portion 15 of the blank 14 isthen expanded, in accordance with the invention as described above, byinjecting a fluid pressure therein through the nozzle 21 and conduit 36connected thereto.

The compressible pressure pad 18 is preferably of a resilient materialsuch as sponge rubber, but any type of rubber-like material is suitable.The pad 18 may be of a nonresilient material such as balsa Wood, butunless the pad is resilient, it will not return to its originalcondition. The hard shim 19 is not mandatory, but if a shim is used agreater cross-sectional area of the normally expanded portion of thetubes, that is the portions 43 at the ends of the panel in FIGURES 6 and7, can be obtained while still producing the desired smooth portions.The compressible pad 18 may be a quarter inch thick medium grade softblock stock industrial sponge rubber pad having a density of about 21pounds per cubic foot, a compressibility of 2 to 5 pounds per squareinch to compress the pad to 75% of its original thickness, and a minimumelongation of 250% backed up by a hard shim .030 inch thick, for a 1100or 28 aluminum blank .060 inch thick, all positioned between hardpressure pads spaced apart .180 inch. The compressible pad may be ofsolid rubber having similar physical characteristics as the previouslydescribed sponge rubber to prevent the compressibility of the pad frombeing affected by liquid spilled thereon. Since the total outwarddistention of the expanded portion of the panel in the area of thesubstantially smooth side is less than the remainder of the expandedportion, the unjoined portion may be wider adjacent the smooth area asindicated by the wider design of the weld-inhibiting material 6.

FIGURES 6 and 7 show opposite sides of the expanded panel 39. In FIGURE6 the conduits 41 each have a wider portion 42 in the area which engagesthe compressible pressure pad 18. The wider portion 42 of the conduitscorresponds to the wider portion 6 of the weldinhibiting pattern shownin FIGURE 1. The conduits 41 have fiat outer surfaces in the area ofengagement with the hard pressure pads 20. With reference to FIGURE 6,it will be seen that the outer portions 43 distend outwardly to agreater extent than do the wide conduit portion 42. Therefore, in orderto assure an adequate cross-sectional area of the conduits 42 thisportion should be wider than the end portions 43, and therefore theweld-inhibiting design shown in FIGURE 1 has a wider midportion 6. Thereverse side of the panel is shown in FIGURE 7, and it will be notedthat the wide portion 42 of the conduits 41 are not distended outwardlyand that the midportion of the panel 39 is smooth. During the expansionof the blank, the pressure of the compressible pressure pad 18 causesthe adjacent portion of the opposite side of the blank to be firmly heldagainst the lower hard pressure pad 20.

After expansion of the unjoined portion 15 of the blank 14 to form thehollow portion of the panel 39, it may be necessary to control therelease of the expansion pressure within the hollow portion and thepressure of a resilient pressure pad 18 against the distended portion ofthe panel, in order to prevent rupturing the panel by the force of theexpansion fluid, and to prevent collapsing the extended hollow portionof the panel through the force of the resilient pressure pad. Byreleasing the pressure in cylinder 26 concurrently with the pressure inthe hollow portion of the panel, any tendency of the pad to collapse thehollow portion or for the expansion pressure to rupture the hollowportion of the panel is retarded.

Although the invention has been described with reference to particularembodiments, materials, and details, various modifications and changeswill be apparent to one skilled in the art, and the invention istherefore not to be limited to such embodiments, materials, or detailsexcept as set forth in the appended claims:

I claim:

1. The method of fabricating a hollow article formed from a blank havingan interconnected unjoined inner portion defined by walls formed ofsheets having different strengths, said method comprising maintainingsaid blank between spaced apart rigid pressure pads with a compressiblepressure pad clamped between one of said rigid pads and the outersurface of the weaker of said sheets throughout and against a limitedarea of said unjoined portion with said limited area encompassing only afraction of said unjoined inner portion, applying within said unjoinedportion a force to distend said blank in the areas defining saidunjoined inner portions, said force being of sufficient magnitude topermanently distend both said sheets in the areas adjacent said limitedarea and the weaker sheet within said limited area but of insufficientmagnitude to permanently distend the stronger sheet within said limitedarea, whereby the portion of said stronger sheet opposite the portion ofsaid weaker sheet adjacent said compressible pressure pad remains smoothupon expansion of said unjoined portion.

2. The method of fabricating a hollow article having partially smoothside and an opposite side having protrusions formed by distentionsconforming to the hollow portion of said article, said method comprisingthe steps of forming a blank by superimposing a first sheet on a secondsheet having an elastic limit differentiable from the elastic limit ofsaid first sheet, joining a portion of said sheets together to define anenclosed interconnected unjoined portion between adjacent surfaces ofsaid sheets, maintaining said blank between spaced apart rigid pressurepads with a compressible pressure pad clamped between one of said rigidpads and the outer surface of the weaker of said sheets throughout andagainst a limited area of said unjoined portion with said limited areaencompassing only a fraction of said unjoined portion, and applying aforce within said unjoined area to outwardly distend both said sheets inthe areas adjacent said limited area and the sheet within said limitedarea having the lower elastic limit, whereby the portion of saidstronger sheet opposite the portion of said weaker sheet adjacent saidcompressible pressure pad remains smooth upon expansion of said unjoinedportion.

3. The method of fabricating a hollow article having partially smoothside and an opposite side having protrusions formed by distentionsconforming to the hollow portion of said article, said method comprisingthe steps of forming a blank by superimposing a first sheet on a secondsheet having an elastic limit differentiable from the elastic limit ofsaid first sheet, joining a portion of said sheets together to define anenclosed interconnected unjoined portion between adjacent surfaces ofsaid sheets, maintaining said blank between spaced apart rigid pressurepads with a compressible pressure pad clamped between one of said rigidpads and the outer surface of the weaker of said sheets throughout andagainst a limited area of said unjoined portion with said limited areaencompassing only a fraction of said unjoined portion, and applyingwithin said unjoined area a force to distend said blank in the areasdefining said unjoined inner portions, said force being of sufiicientmagnitude to distend both said sheets in the areas adjacent said limitedarea and the weaker sheet beyond its elastic limit within said limitedarea but of insufficient magnitude to distend the stronger sheet beyondits elastic limit in the area of said compressible pressure pad, wherebythe portion of said stronger sheet opposite said compressible pressurepad remains smooth upon expansion of said unjoined portion.

4. The method of fabricating a hollow article having partially smoothside and an opposite side having protrusions formed by distentionsconforming to the hollow portion of said article, said method comprisingthe steps of forming a blank by superimposing a first sheet on a secondsheet having an elastic limit differentiable from the elastic limit ofsaid first sheet of material amenable to a heat treatment affecting theelastic limit of said sheet, said first sheet also being of a materialamenable to heat treatment alfecting its elastic limit in about the samerange of temperature for treating said second sheet, joining a portionof said sheets together to define an enclosed interconnected unjoinedportion between adjacent surfaces of said sheets, heat treating saidjoined sheets to reduce the elastic limit of the sheet initially havingthe lower limit and to raise the elastic limit of the sheet initiallyhaving the higher limit, maintaining said blank between spaced apartrigid pressure pads with a compressible pressure pad clamped between oneof said rigid pads and the outer surface of the weaker of said sheetsthroughout and against a limited area of said unjoined portion with saidlimited area encompassing only a fraction of said un joined portion, andapplying within said unjoined portion a force to distend said blank inthe areas defining said unjoined inner portion, said force being ofsuflicient magnitude to distend both said sheets in the areas adjacentsaid limited area and the weaker sheet beyond its elastic limit withinsaid limited area but of insufiicient magnitude to distend the strongersheet beyond its elastic limit within the area of said compressiblepressure pad, whereby the portion of said stronger sheet opposite saidcompressible pressure pad remains smooth upon expansion of said unjoinedportion.

UNITED STATES. PATENTS Whistler Dec. 29, 1936 Pease Feb. 22, 1944 RoodAug, 23, 1949 Schoellerman Jan. 15, 1952 Howenstine June 10, 1952Grenell Sept. 28, 1954 Clevenger et a1 Dec. 27, 1955 Engel June 12, 1956Schuster Jan; 29, 1957 Fentress Feb. 4, 1958 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No, 3,067,491 December 11, 1962 RobertM. Neel et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

In the grant, lines 1 to 3, for "Robert M. Neel, of New Douglas, andUlric R. Jaeger, of'Alton, Illinois, and Clarence A. Isbell, Jr,, ofFerguson, Missouri,"- read Robert M. Neel, of New Douglas, and Ulric R,Jaeger, of Alton, Illinois, and Clarence A. Isbell, Jr., of Ferguson,Missouri, assignors to Olin Mathieson Chemical Corporation, of EastAlton, Illinois, a corporation of Virginia, lines 12 and 13, for "RobertM. Neel, Ulric R. Jaeger, and Clarence A, Isbell, Jr. their heirs" readOlin Mathieson Chemical Corporation, its successors in the heading tothe printed specification, lines 3 and 4, for "Robert M. Neel, NewDouglas, andUlric R, Jaeger,Alton, 111., and Clarence A, Isbell,

Jr-,, Ferguson, Mo," read Robert M. Neel, New Douglas, and Ulric R.Jaeger, Alton, Ill, and Clarence Ao Isbell, Jr. Ferguson, M0,, assignorsto Olin Mathieson Chemical Corporation, East Alton, Ill, a corporationof Virginia Signed and sealed this 18th day of June 1963o (SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

